The present invention relates to non-magnetic material for magnetic head, and particularly to non-magnetic ceramic substrate material having increased lifetime by preventing exfoliation and crack of the magnetic thin film through using material for non-magnetic ceramic substrate having similar thermal expansivity to the metal magnetic thin film, low abrasion during contact travel of magnetic tape and good processability.
Recently, VTR head comes to have high performance as the function of the VTR comes to have high recording density.
Particularly, for the D-VTR (digital VTR) in which the velocity of the tape is faster than the conventional VTR, integrated head having low perturbation noise is used.
As for the conventional material for non-magnetic substrate material for such a head, barium titanate (BaTiO.sub.3), calcium titanate (CaTiO.sub.3), etc. are used.
However, since such material has thermal expansivity of 90-110.times.10.sup.-7 /.degree. C. which is lower than that of sendust or Fe based metal thin film material (120-150.times.10.sup.-7 /.degree. C.) which was used as the metal magnetic thin film, exfoliation or crack of the metal magnetic thin film is produced. And these deteriorate electromagnetic characteristic of the magnetic head and lower processing yield.
To solve the above-mentioned problems, recently, CoO-NiO based material (Japanese Laid open Patent hei 3-80412) and MnO-NiO based material (Japanese Laid open Patent hei 4-95204) were applied to form non-magnetic substrate material which have thermal expansivity of 120-150.times.10.sup.-7 /.degree. C.
In the Japanese Laid open Patent hei 3-80412, Co.sub.x Ni.sub.1-x O.sub.2 (0.ltoreq.x.ltoreq.0.2), non-magnetic substrate material having rock salt-type structure is disclosed. The material has thermal expansivity of about 150.times.10.sup.-7 /.degree. C. and hardness of about 500-700 by Vikers.
In this Patent, material having no chipping and good processability could be obtained by using CoO-NiO based hot press and by manufacturing particle size thereof to 5 .mu.m or less.
In the Japanese Laid open Patent hei 4-95204, MnNiO.sub.2 having rock salt-type crystal structure is used as the non-magnetic substrate material. In this material 20-40 mol % of MnO, 50-80 mol % of NiO are contained as main components and one or more Y.sub.2 O.sub.3, CaO, Al.sub.2 O.sub.3, ZrO.sub.2, etc. are contained to improve sintering characteristic and to adjust particle diameter. The thermal expansivity at this time is about 130-140.
In this patent, non-magnetic substrate consisting of 77-98 mol % of MnO as a main component and 2-23 mol % of TiO.sub.2 is disclosed. At this time, if the amount of MnO is less than 77%, the expansivity is less than 100.times.10.sup.-7 and so the thermal expansivity of the metal magnetic thin film and non-magnetic substrate material could not coincide and if the amount of MnO exceeds 98%, pores having 5 .mu.m or over come to be produced and sintering characteristic is deteriorated.
To improve this problem, 2-23 mol % of TiO.sub.2 is added to MnO to eliminate the pores and to improve sintering characteristic.
However, since the above-mentioned material such as barium titanate, calcium titanate, etc. have different thermal expansivity with the metal magnetic film, exfoliation or crack of the metal magnetic thin film is produced and this deteriorates electromagnetic characteristic and processing yield of magnetic head. And though CoO-NiO based material or MnO-NiO based material has high thermal expansivity, since their abrasion resistance are low, lifetime of the head decreases with the increase of the abrasion amount when travel velocity of tape is increased.